Plant adenylosuccinate synthetase and DNA coding therefor

ABSTRACT

The present invention provides novel plant DNA sequences coding for native adenylosuccinate synthetase (ADSS). Methods for using the complete or partial ADSS coding sequence as a probe for diagnostic, mapping and other purposes are taught. Generation of transformed host cells capable of expressing ADSS is also taught. Methods of using the transformed host cells are taught, including methods for recombinant production of ADSS enzymes. A method for using the plant ADSS enzyme to screen for inhibitors of ADSS activity is also provided.

This is a continuation of Ser. No. 08/612,033, filed Mar. 7, 1996, now abandoned, which is a divisional of Ser. No. 08/361,611, filed, Dec. 22, 1994, issued as U.S. Pat. No. 5,519,125.

FIELD OF THE INVENTION

The invention relates generally to an enzymatic activity involved in adenosine 5'-monophosphate biosynthesis in plants. In particular, the invention relates to the plant enzyme which catalyzes the synthesis of adenylosuccinate and the gene encoding this enzyme. In one aspect, the invention relates to the recombinant production of this enzyme in a heterologous host. In another aspect, the invention is applied to the identification of new herbicides. In yet another aspect, the invention relates to the development of genetic markers in plants.

BACKGROUND OF THE INVENTION

Adenosine 5'-monophosphate (AMP, also known as adenylic acid) is a precursor of adenosine 5'-triphosphate (ATP), the key energy carrying molecule for all living systems. The first committed enzymatic step in the biosynthesis of AMP is the synthesis of adenylosuccinate from inosine 5'-monophosphate (IMP; inosinic acid) and aspartate. The enzyme which catalyzes this step is known as adenylosuccinate synthetase (IMP:L-aspartate ligase(GDP-forming), EC 6.3.4.4, referred to herein as "ADSS").

In E. coli, ADSS is a dimer of identical 48 kD subunits. Its three-dimensional structure has been determined to 2.8 Å resolution (Poland et al., J Biol. Chem. 268:25334-25342 (1993). In mammalian cells, the ADSS enzyme is present as two isoforms. An acidic form, present in non-muscle tissues, is thought to be involved in de novo production of AMP. A basic form, present in muscle tissue, thought to act as part of the purine nucelotide cycle, which involves interconversion of IMP and AMP with the net result of deaminating aspartate to fumarate (Lehninger, Biochemistry. Worth Publishers, NY (1975), p. 743; Lowenstein, Int. J. Sports Med.11: S36-S46 (1990).

Genes encoding the ADSS enzyme have been isolated from a variety of species including E. coli (Wolfe and Smith, J. Biol. Chem. 263: 19147-19153 (1988)), D. discoideum (Weismuller et al., J Biol. Chem. 266: 2480-2485 (1991)), mouse (Guicherit et al., J Biol. Chem. 266: 22582-22587 (1991); Guicherit et al., J. Biol. Chem. 269: 4488-4496 (1994), Bacillus subtilus (Maentsaelae and Zalkin, J. Bacteriol. 174: 1881-1890 (1992), human (Powell et al., FEBS Lett. 303: 4-10 (1992), S. cerevisiae (Genbank accession no. L22185), and Caenorhabditis elegans (EST; Genbank accession no. M75738). However, genes encoding the ADSS enzyme have heretofore not been isolated from any plant species.

Presently, too little is known about the plant ADSS enzyme and its relationship to the ADSS enzymes/genes which have been isolated from other organisms to allow isolation of ADSS encoding genes from any plant species using known approaches.

Methods for isolating genes which are based upon knowledge of the structure of the proteins they encode cannot be applied to plant ADSS genes because too little is presently known about plant ADSS enzymes. Metabolic enzymes such as ADSS are typically very difficult to purify from plants because of their extremely low abundance. In addition, the presence of various phenolic and carbohydrate compounds in plants can interfere with the isolation of pure enzyme with native activity.

In the absence of direct structural information, a number of standard techniques are available for the isolation of proteins and their corresponding genes. Such standard techniques include nucleic acid hybridization and amplification by polymerase chain reaction using oligonucleotide primers corresponding to conserved amino acid sequence motifs. Unfortunately, these techniques would not be expected to be useful for isolation of plant ADSS genes because they rely upon the presence of significant structural similarity (i.e. amino acid and DNA sequence) with known proteins and genes that have the same function. Since there is no significant structural similarity even among the known ADSS genes and proteins from non-plant organisms (see, e.g. Powell et al., FEBS Lett. 303: 4-10 (1992)) it is unlikely that these proteins would share any significant structural similarity with plant ADSS proteins.

Another approach that has been used to isolate biosynthetic genes in other metabolic pathways from higher eukaryotes is the complementation of microbial mutants deficient in the activity of interest. For this approach, a library of cDNAs from the higher eukaryote is cloned in a vector that can direct expression of the cDNA in the microbial host. The vector is then transformed or otherwise introduced into the mutant microbe, and colonies are selected that are phenotypically no longer mutant.

This strategy has worked for isolating genes from higher eukaryotes that are involved in several metabolic pathways, including histidine biosynthesis (e.g. U.S. patent application Ser. No. 08/061,644 to Ward et al., incorporated by reference herein in its entirety), lysine biosynthesis (e.g. Frisch et al., Mol. Gen. Genet. 228: 287 (1991)), purine biosynthesis (e.g. Aimi et al., J Biol. Chem. 265: 9011 (1990)), and tryptophan biosynthesis (e.g. Niyogi et al., Plant Cell 5: 1011 (1993)). This strategy has also been used to isolate plant genes including those coding for maize glutamine synthase (Snustad et al, Genetics 120:1111-1114 (1988)), soybean-pyrroline-5-carboxylate reductase (Delauney et al., Mol. Genet. 221:299-305 (1990), maize dihydrodipicolinate synthase (Frisch et al., Mol. Gen. Genet. 228:287-293(1991)), rape chloroplast 3-isopropylmalate dehydrogenase (Eller et al., Plant Mol. Biol. 18:557-566 (1992); Proc. Natl. Acad. Sci, USA 88:1731-1735 (1991)), and dihydroorotate dehydrogenase (Minet et al., Plant J. 2:417-422 (1992)).

Microbial mutants thought to be defective in ADSS activity are available (e.g. E. coli purA mutant designated CGCS 5408 and E. coli strains CGCS 4431 and 7039 from E. coli Genetic Stock Center, Yale Univ.; yeast ade 12 mutants reported in Dorfman, Genetics 61:377-389 (1969)). However, despite the availability of these mutants, application of the complementation technique to isolate cDNAs encoding ADSS enzymatic activity has proven to be unsuccessful for avian (Powell et al, FEBS Lett. 303: 4-10 (1992)) and B. subtilis ADSS (Maentsaelae and Zalkin, J. Bacteriol. 174: 1881-1890 (1992).

There are several reasons which may explain the failure of this complementation strategy when applied to ADSS, particularly eukaryotic ADSS genes. First, the eukaryotic ADSS cDNA sequence may not be expressed at adequate levels in the mutant microbe, for instance because of codon usage inconsistent with the usage preferences of the microbial host. Second, the primary translation product from the cloned eukaryotic coding sequence may not produce a functional polypeptide, for instance if activity requires a post-translational modification, such as glycosylation, that is not carried out by the microbe. Third, the heterologous protein expressed in E. coli may also be lethal to the cells in which it is expressed, thus rendering its isolation impossible. Fourth, the eukaryotic protein may fail to assume its active conformation in the microbial host, for instance if the protein is normally targeted to a specific organellar membrane system that the microbial host specifically lacks. This last possibility is especially likely for the plant ADSS enzyme, which has been associated in the plant cell with organelles not present in microbial hosts used in the complementation assay (Schubert, Annu. Rev. Plant Physiol. 37:539-574 (1986), and presumably reaches that organellar system as a result of a post-translational targeting mechanism involving both an N-terminal transit sequence, and intrinsic properties of the mature polypeptide (see, e.g. Kohorn and Tobin, Plant Cell 1: 159 (1989); Li et al., Plant Cell 3: 709 (1991); Li et al., J. Biol. Chem. 267: 18999 (1992)). Moreover, two other purine biosynthetic genes isolated from plants, 5'-phosphoribosyl-5-aminoimdazole synthetase (Senecoff and Meagher, Plant Physiol. 102:387-399 (1993)) and glycinamide synthetase (Schnorr et al., Plant J. 6:113-121 (1994)) also appear encode proteins that are targeted to the chloroplast.

SUMMARY OF THE INVENTION

The present invention provides an isolated DNA molecule encoding the adenylosuccinate synthetase (ADSS) enzyme from a plant source.

The DNA coding sequences for ADSS enzymes in Arabidopsis thaliana and Zea mays are provided in SEQ ID NOS: 1 and 3, respectively. Using the information provided by the present invention, the DNA coding sequence for the adenylosuccinate synthetase (ADSS) enzyme from any plant source may now be obtained using standard methods.

The present invention also encompasses the recombinant production of the ADSS enzyme, and methods for using recombinantly produced ADSS. In particular, the present invention provides methods of using purified ADSS to screen for novel herbicides which affect the activity of ADSS.

The present invention is further directed to probes and methods for detecting the presence and form of the ADSS gene and quantitating levels of ADSS transcripts in an organism. These methods may be used to diagnose disease conditions which are associated with an altered form of the ADSS enzyme or altered levels of expression of the ADSS enzyme.

DETAILED DESCRIPTION OF THE INVENTION

In one aspect, the present invention is directed to an isolated DNA molecule which encodes a eukaryotic form of adenylosuccinate synthetase (referred to herein as "ADSS"), the enzyme which catalyzes the synthesis of adenylosuccinate from IMP. The DNA coding sequence and corresponding amino acid sequence for an ADSS enzyme from Arabidopsis thaliana is provided as SEQ ID NOS:1 and 2, respectively. The DNA coding sequence and corresponding amino acid sequence for a maize ADSS enzyme is provided as SEQ ID NOS:3 and 4, respectively.

The DNA encoding the ADSS enzyme may be isolated from the genome of any plant species desired according to the invention. One method taught for isolating a plant ADSS coding sequence is represented by Example 1. In this method cDNA clones encoding an ADSS enzyme are identified from a library of cDNA clones derived from the eukaryote of interest based on their ability to supply ADSS enzymatic activity to a mutant host organism deficient in this activity. Suitable host organisms for use in this method are those which can be used to screen cDNA expression libraries and for which mutants deficient in ADSS activity are either available or can be routinely generated. Such host organisms include, but are not limited to, E. coli and yeast.

Alternatively, plant ADSS coding sequences may be isolated according to well known techniques based on their sequence homology to the Arabidopsis thaliana (SEQ ID NO:1) and Zea mays (SEQ ID NO:3) ADSS coding sequences taught by the present invention. In these techniques all or part of the known ADSS coding sequence is used as a probe which selectively hybridizes to other ADSS coding sequences present in population of cloned genomic DNA fragments or cDNA fragments (i.e. genomic or cDNA libraries) from a chosen organism. Such techniques include hybridization screening of plated DNA libraries (either plaques or colonies; see, e.g. Sambrook et al., "Molecular Cloning", eds., Cold Spring Harbor Laboratory Press. (1989)) and amplification by PCR using oligonucleotide primers corresponding to sequence domains conserved among known ADSS amino acid sequences (see, e.g. Innis et al., "PCR Protocols, a Guide to Methods and Applications", pub. by Academic Press (1990)). These methods are particularly well suited to the isolation of ADSS coding sequences from organisms closely related to the organism from which the probe sequence is derived. Thus, application of these methods using the Arabidopsis or Zea mays coding sequence as a probe would be expected to be particularly well suited for the isolation of ADSS coding sequences from other plant species.

The isolated plant ADSS sequences taught by the present invention may be manipulated according to standard genetic engineering techniques to suit any desired purpose. For example, the entire ADSS sequence or portions thereof may be used as probes capable of specifically hybridizing to ADSS coding sequences and messenger RNAs. To achieve specific hybridization under a variety of conditions, such probes include sequences that are unique among ADSS coding sequences and are preferably at least 10 nucleotides in length, and most preferably at least 20 nucleotides in length. Such probes may be used to amplify and analyze ADSS coding sequences from a chosen organism via the well known process of polymerase chain reaction (PCR). This technique may be useful to isolate additional ADSS coding sequences from a desired organism or as a diagnostic assay to determine the presence of ADSS coding sequences in an organism. This technique may also be used to detect the presence of altered ADSS coding sequences in a plant associated with a particular condition of interest such as herbicide resistance, AMP deficiency, poor health, etc.

ADSS specific hybridization probes may also be used to map the location of the native ADSS gene(s) in the genome of a chosen plant using standard techniques based on the selective hybridization of the probe to genomic ADSS sequences. These techniques include, but are not limited to, identification of DNA polymorphisms identified or contained within the ADSS probe sequence, and use of such polymorphisms to follow segregation of the ADSS gene relative to other markers of known map position in a mapping population derived from self fertilization of a hybrid of two polymorphic parental lines (see e.g. Helentjaris et al., Plant Mol. Biol. 5: 109 (1985); Sommer et al. Biotechniques 12:82 (1992); D'Ovidio et al., Plant Mol. Biol. 15: 169 (1990)). While any plant ADSS sequence is contemplated to be useful as a probe for mapping ADSS genes, preferred probes are those ADSS sequences from plant species more closely related to the chosen plant species, and most preferred probes are those ADSS sequences from the chosen plant species. Mapping of ADSS genes in this manner is contemplated to be particularly useful for breeding purposes. For instance, by knowing the genetic map position of a mutant ADSS gene that confers herbicide resistance, flanking DNA markers can be identified from a reference genetic map (see, e.g., Helentjaris, Trends Genet. 3: 217 (1987)). During introgression of the herbicide resistance trait into a new breeding line, these markers can then be used to monitor the extent of ADSS-linked flanking chromosomal DNA still present in the recurrent parent after each round of back-crossing.

ADSS specific hybridization probes may also be used to quantitate levels of ADSS mRNA in a plant using standard techniques such as Northern blot analysis. This technique may be useful as a diagnostic assay to detect altered levels of ADSS expression that may be associated with particular conditions such as deficiencies in adenylosuccinate or AMP levels or enhanced tolerance to herbicides which target ADSS.

For recombinant production of the enzyme in a host organism, the plant ADSS coding sequence may be inserted into an expression cassette designed for the chosen host and introduced into the host where it is recombinantly produced. The choice of specific regulatory sequences such as promoter, signal sequence, 5' and 3' untranslated sequences, and enhancer appropriate for the chosen host is within the level of skill of the routineer in the art. The resultant molecule, containing the individual elements linked in proper reading frame, may be inserted into a vector capable of being transformed into the host cell. Suitable expression vectors and methods for recombinant production of proteins are well known for host organisms such as E. coli (see, e.g Studier and Moffatt, J. Mol. Biol. 189: 113 (1986); Brosius, DNA 8: 759 (1989)), yeast (see, e.g., Schneider and Guarente, Meth. Enzymol. 194: 373 (1991)) and insect cells (see, e.g., Luckow and Summers, Bio/Technol. 6: 47 (1988)). Specific examples include plasmids such as pBluescript (Stratagene, La Jolla, Calif.), pFLAG (International Biotechnologies, Inc., New Haven, Conn.), pTrcHis (Invitrogen, La Jolla, Calif.), and baculovirus expression vectors, e.g., those derived from the genome of Autographica californica nuclear polyhedrosis virus (AcMNPV). A preferred baculovirus/insect system is pV111392/Sf21 cells (Invitrogen, La Jolla, Calif.).

Recombinantly produced plant ADSS enzyme can be isolated and purified using a variety of standard techniques. The actual techniques which may be used will vary depending upon the host organism used, whether the ADSS enzyme is designed for secretion, and other such factors familiar to the skilled artisan (see, e.g. chapter 16 of Ausubel, F. et al., "Current Protocols in Molecular Biology", pub. by John Wiley & Sons, Inc. (1994).

Recombinantly produced plant ADSS enzyme is useful for a variety of purposes. For example, it may be used to supply ADSS enzymatic activity in vitro to synthesize adenylosuccinate. In vitro synthesis of adenylosuccinate may be accomplished by reacting IMP, GTP, and aspartate in the presence of ADSS enzyme in an appropriate buffer, containing a divalent cation such as Mg²⁺ (see, e.g. Baugher et al. Biochem. Biophys. Res. Commun. 94:123-129 (1980); Stayton et al. Curr. Top. Cell. Regul. 22.103-141 (1983); Bass et al., Arch. Biochem. Biophys. 256:335-342 (1987)). The adenylosuccinate produced is a useful reagent which may be used as a substitute for purified adenylosuccinic acid previously available commercially from other sources.

Recombinantly produced plant ADSS enzyme may also be used in an in vitro assay to screen known herbicidal chemicals whose target has not been identified to determine if they inhibit ADSS. Such an in vitro assay may also be used as a more general screen to identify chemicals which inhibit ADSS activity and which are therefore herbicide candidates. Alternatively, recombinantly produced ADSS may be used to elucidate the complex structure of this enzyme. Such information regarding the structure of the ADSS enzyme may be used, for example, in the rational design of new inhibitory herbicides.

Typically, the inhibitory effect on ADSS is determined by a reduction or complete inhibition of adenylosuccinate synthesis in the in vitro assay (see, e.g. Baugher et al. Biochem. Biophys. Res. Commun. 94:123-129 (1980); Stayton et al. Curr. Top. Cell. Regul. 22:103-141 (1983); Bass et al., Arch. Biochem. Biophys. 256:335-342 (1987)). Such a determination may be made simply by comparing the amount of adenylosuccinate synthesized in the in vitro assay in the presence and absence of the candidate inhibitor.

The invention will be further described by reference to the following detailed examples. These examples are provided for purposes of illustration only, and are not intended to be limiting unless otherwise specified.

EXAMPLES

Standard recombinant DNA and molecular cloning techniques used here are well known in the art and are described by T. Maniatis, E. F. Fritsch and J. Sambrook, Molecular Cloning: A Laboratory manual, Cold Spring Harbor laboratory, Cold Spring Harbor, N.Y. (1982) and by T. J. Silhavy, M. L. Berman, and L. W. Enquist, Experiments with Gene Fusions, Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y. (1984) and by Ausubel, F. M. et al., Current Protocols in Molecular Biology, pub. by Greene Publishing Assoc. and Wiley-Interscience (1987).

Example 1

Isolation of Arabidopsis cDNAs encoding ADSS genes by functional complementation of an E. coli mutant.

An Arabidopsis thaliana (Landsberg) cDNA library in the plasmid vector pFL61 (Minet et al., PlantJ. 2:417-422 (1992)) was obtained and amplified. The E. coli purA mutant PC0543 (CGSC #5408; E. coli Genetics Stock Center, Yale University, New Haven, Conn.) was obtained and maintained on N agar. The plasmid libraries were transformed into CGSC #5408 by electroporation using the Bio-Rad Gene Pulser and the manufacturer's conditions. The cells were plated on minimal E agar (Vogel and Bonner, J Biol. Chem. 218:97-106 (1956) containing 100 mg/ml ampicillin and 0.4% casamino acids at a density of approximately 10,000,000 transformants/10 cm plate. Adenine prototrophs were recovered at a frequency of 1/6×10⁷ from the pFL61 library. Plasmid DNA was isolated form the colony for sequence analysis. Purified plasmid DNA was shown to transform CGSC #5408 to purine prototrophy at high frequency. The purified plasmid complemented two additional E. coli purA mutants: ES4 (CGSC #4431; E. coli Genetics Stock Center, Yale University, New Haven, Conn.) and TX595 (CGSC #7039; E. coli Genetics Stock Center, Yale University, New Haven, Conn.), further confirming that it encoded a functional ADSS enzyme.

A restriction digest revealed that the cDNA insert was greater than 3 kB; sequence analysis revealed that the cDNA was chimeric, containing at the 3' end 1512 bp preceded by a poly A region. This 1512 bp region encodes an incomplete ADSS containing the mature protein sequence and a partial probable chloroplast transit peptide. A database search with the GAP program (Deveraux et al., Nucleic Acids Res. 12:387-395 (1984) reveals homology with the ADSS from S. cerevisiae. The two proteins are 70% similar, 51% identical with regions of high homology. The protein is 65% similar, 44% identical with E. coli ADSS.

ADSS-1, in the pBluescript SK vector, was deposited Sep. 22, 1994 as pWDC-6 (NRRL #B-21328).

The Arabidopsis cDNA sequence encoding ADSS-1 contained in pWDC-6 is set forth in SEQ ID NO:1. The ADSS-1 amino acid sequence encoded by this cDNA is set forth in SEQ ID NO:2.

Example 2

Isolation of Maize cDNAs encoding ADSS genes based on sequence homology to Arabidopsis ADSS.

A custom-made Unizap Zea Mays (cv. Blizzard) cDNA library was purchased from Clontech. Approximately 160,000 pfu of the phage library was plated at a density of 8,000 plaques per 10 cm Petri dish, and duplicate filter lifts were made onto nitrocellulose membrane (Scheiller and Scheull) after approximately 7 hours growth at 37°. The filter lifts were probed with a PCR amplified fragment of the Arabidopsis ADSS cDNA labeled with ³² P-dCTP by the random priming method (Life Technologies, Bethesda, Md.). Hybridization and wash conditions were at 50° as described in Church and Gilbert, 1984. After purification to single positively hybridizing plaques, plasmids were in vivo excised and cDNA inserts sequenced using dideoxy terminators labeled with fluorescent dyes (Applied Biosystems, Inc., Foster City, Calif.). The sequence thus obtained for the maize ADSS cDNA and the protein it encodes are provided as SEQ ID NOS:3 and 4, respectively.

Example 3

Isolation of additional ADSS genes based on sequence homology to known ADSS coding sequences

A phage or plasmid library is plated at a density of approximately 10,000 plaques on a 10 cm Petri dish, and filter lifts of the plaques are made after overnight growth of the plates at 37° C. The plaque lifts are probed with one of the cDNAs set forth in SEQ ID NOS:1 or 3, labeled with 32P-dCTP by the random priming method by means of a PrimeTime kit (International Biotechnologies, Inc., New Haven, Conn.). Hybridization conditions are 7% sodium dodecyl sulfate (SDS), 0.5M NaPO4 pH 7.0, 1 mM EDTA at 50° C. After hybridization overnight, the filters are washed with 2× SSC, 1% SDS. Positively hybridizing plaques are detected by autoradiography. After purification to single plaques, cDNA inserts are isolated, and their sequences determined by the chain termination method using dideoxy terminators labeled with fluorescent dyes (Applied Biosystems, Inc., Foster City, Calif.).

The standard experimental protocol described above can be used by one of skill in the art to obtain ADSS genes sequentially homologous to the known ADSS coding sequences from any other eukaryote, particularly other higher plant species.

An alignment of the predicted amino acid sequences of the respective proteins encoded by the nucleotide sequences shown in SEQ ID NOS:1 and 3 are set forth in Table 1.

                                      TABLE 1     __________________________________________________________________________     Comparison of the Arabidopsis (SEQ ID NO: 2) and     Maize (SEQ ID NO: 4) ADSS-1 Amino Acid Sequences     Identical residues are denoted by the vertical bar between the two     sequences. Alignment is     performed using the GAP program described in Deveraux et al., Nucleic     Acids Res. 12:387-395     (1984).     __________________________________________________________________________      ##STR1##      ##STR2##      ##STR3##      ##STR4##      ##STR5##      ##STR6##      ##STR7##      ##STR8##      ##STR9##      ##STR10##     __________________________________________________________________________

Various modifications of the invention described herein will become apparent to those skilled in the art. Such modifications are intended to fall within the scope of the appended claims.

    __________________________________________________________________________     SEQUENCE LISTING     (1) GENERAL INFORMATION:     (iii) NUMBER OF SEQUENCES: 4     (2) INFORMATION FOR SEQ ID NO:1:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 1516 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (iii) HYPOTHETICAL: NO     (ix) FEATURE:     (A) NAME/KEY: CDS     (B) LOCATION: 1..1470     (D) OTHER INFORMATION: /product= "Arabidopsis     Adenylosuccinate Synthetase"     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:     ATGTCTCTCTCTTCCCTCACTCTCGACTCCAATCCAAGATTCGCTGTT48     MetSerLeuSerSerLeuThrLeuAspSerAsnProArgPheAlaVal     151015     GGTGGACCTTATCACCGCCGTTATCCTCCTCTTCACCACCCTCGAAGC96     GlyGlyProTyrHisArgArgTyrProProLeuHisHisProArgSer     202530     TTCGTCTCTTGCTCTGCTAAACGTCCAGCTGTCTCCGCTTCACTGAGC144     PheValSerCysSerAlaLysArgProAlaValSerAlaSerLeuSer     354045     GTCGCCGCTGATTCAGCCGCCACTGAGTCTCTTGGACGGATTGGATCA192     ValAlaAlaAspSerAlaAlaThrGluSerLeuGlyArgIleGlySer     505560     CTGAGTCAAGTATCTGGTGTACTCGGTTGCCAATGGGGAGATGAAGGT240     LeuSerGlnValSerGlyValLeuGlyCysGlnTrpGlyAspGluGly     65707580     AAAGGCAAACTCGTTGACATCTTAGCCCAACACTTTGACATCGTTGCT288     LysGlyLysLeuValAspIleLeuAlaGlnHisPheAspIleValAla     859095     CGTTGTCAGGGTGGAGCTAATGCTGGACACACTATATACAATTCAGAG336     ArgCysGlnGlyGlyAlaAsnAlaGlyHisThrIleTyrAsnSerGlu     100105110     GGAAAGAAATTTGCACTTCACCTTGTGCCTTCAGGTATCCTGAATGAG384     GlyLysLysPheAlaLeuHisLeuValProSerGlyIleLeuAsnGlu     115120125     GATACTACTTGTGTCATTGGAAACGGAGTTGTGGTGCATTTGCCAGGT432     AspThrThrCysValIleGlyAsnGlyValValValHisLeuProGly     130135140     CTCTTCAAAGAGATTGATGGTTTGGAGTCCAATGGTGTCTCCTGTAAA480     LeuPheLysGluIleAspGlyLeuGluSerAsnGlyValSerCysLys     145150155160     GGAAGGATTTTGGTCTCTGATCGCGCTCACTTGTTATTCGATTTCCAT528     GlyArgIleLeuValSerAspArgAlaHisLeuLeuPheAspPheHis     165170175     CAAGAGGTTGATGGGCTCAGGGAATCTGAGCTTGCCAAGTCGTTCATT576     GlnGluValAspGlyLeuArgGluSerGluLeuAlaLysSerPheIle     180185190     GGCACCACCAAGAGGGGAATTGGTCCTGCCTACTCTAGTAAAGTGATA624     GlyThrThrLysArgGlyIleGlyProAlaTyrSerSerLysValIle     195200205     AGGAATGGTATTAGAGTAGGTGATCTCAGGCACATGGATACTTTACCT672     ArgAsnGlyIleArgValGlyAspLeuArgHisMetAspThrLeuPro     210215220     CAAAAGCTTGACCTTTTACTATCAGATGCAGCGGCAAGGTTTCAAGGG720     GlnLysLeuAspLeuLeuLeuSerAspAlaAlaAlaArgPheGlnGly     225230235240     TTCAAGTATACTCCTGAAATGCTTCGGGAAGAAGTTGAAGCATACAAG768     PheLysTyrThrProGluMetLeuArgGluGluValGluAlaTyrLys     245250255     AGATACGCTGACAGATTGGAGCCCTACATTACTGACACTGTCCATTTC816     ArgTyrAlaAspArgLeuGluProTyrIleThrAspThrValHisPhe     260265270     ATCAATGACTCGATTTCGCAGAAGAAAAAGGTTTTGGTCGAAGGTGGT864     IleAsnAspSerIleSerGlnLysLysLysValLeuValGluGlyGly     275280285     CAAGCTACAATGTTGGACATTGACTTTGGGACTTATCCTTTTGTTACT912     GlnAlaThrMetLeuAspIleAspPheGlyThrTyrProPheValThr     290295300     TCCTCCAGCCCCTCAGCCGGTGGGATCTGCACAGGTCTTGGTATTGCA960     SerSerSerProSerAlaGlyGlyIleCysThrGlyLeuGlyIleAla     305310315320     CCAAGTGTTGTTGGTGATCTAATTGGAGTGGTAAAAGCATACACTACA1008     ProSerValValGlyAspLeuIleGlyValValLysAlaTyrThrThr     325330335     AGAGTTGGTTCAGGTCCATTCCCGACAGAAAATTTGGGCACAGGTGGT1056     ArgValGlySerGlyProPheProThrGluAsnLeuGlyThrGlyGly     340345350     GACCTTCTTAGGTTAGCTGGACAGGAGTTTGGCACTACAACTGGTCGT1104     AspLeuLeuArgLeuAlaGlyGlnGluPheGlyThrThrThrGlyArg     355360365     CCTCGTCGGTGTGGCTGGCTTGACATTGTTGCCCTGAAATTTTCTTGC1152     ProArgArgCysGlyTrpLeuAspIleValAlaLeuLysPheSerCys     370375380     CAAATCAATGGATTTGCATCACTTAATCTCACTAAGCTTGATGTACTT1200     GlnIleAsnGlyPheAlaSerLeuAsnLeuThrLysLeuAspValLeu     385390395400     TCGGATCTGAACGAAATCCAGCTGGGTGTGGCTTACAAGAGGAGTGAC1248     SerAspLeuAsnGluIleGlnLeuGlyValAlaTyrLysArgSerAsp     405410415     GGCACCCCTGTTAAATCATTCCCTGGTGATCTTCGTCTTCTCGAAGAA1296     GlyThrProValLysSerPheProGlyAspLeuArgLeuLeuGluGlu     420425430     CTGCATGTGGAGTATGAAGTCTTACCTGGGTGGAAGTCTGACATATCC1344     LeuHisValGluTyrGluValLeuProGlyTrpLysSerAspIleSer     435440445     TCGGTCAGAAACTACTCTGATCTTCCAAAGGCTGCTCAGCAATATGTT1392     SerValArgAsnTyrSerAspLeuProLysAlaAlaGlnGlnTyrVal     450455460     GAGAGGATTGAAGAACTCGTGGGTGTGCCCATTCATTACATTGGTATT1440     GluArgIleGluGluLeuValGlyValProIleHisTyrIleGlyIle     465470475480     GGGCCCGGTCGTGATGCCCTTATATATAAATGATTTTTAGTGTTAGGCTT1490     GlyProGlyArgAspAlaLeuIleTyrLys     485490     TTTTGGTTCCTCCACAAACTCAAAAT1516     (2) INFORMATION FOR SEQ ID NO:2:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 490 amino acids     (B) TYPE: amino acid     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: protein     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:     MetSerLeuSerSerLeuThrLeuAspSerAsnProArgPheAlaVal     151015     GlyGlyProTyrHisArgArgTyrProProLeuHisHisProArgSer     202530     PheValSerCysSerAlaLysArgProAlaValSerAlaSerLeuSer     354045     ValAlaAlaAspSerAlaAlaThrGluSerLeuGlyArgIleGlySer     505560     LeuSerGlnValSerGlyValLeuGlyCysGlnTrpGlyAspGluGly     65707580     LysGlyLysLeuValAspIleLeuAlaGlnHisPheAspIleValAla     859095     ArgCysGlnGlyGlyAlaAsnAlaGlyHisThrIleTyrAsnSerGlu     100105110     GlyLysLysPheAlaLeuHisLeuValProSerGlyIleLeuAsnGlu     115120125     AspThrThrCysValIleGlyAsnGlyValValValHisLeuProGly     130135140     LeuPheLysGluIleAspGlyLeuGluSerAsnGlyValSerCysLys     145150155160     GlyArgIleLeuValSerAspArgAlaHisLeuLeuPheAspPheHis     165170175     GlnGluValAspGlyLeuArgGluSerGluLeuAlaLysSerPheIle     180185190     GlyThrThrLysArgGlyIleGlyProAlaTyrSerSerLysValIle     195200205     ArgAsnGlyIleArgValGlyAspLeuArgHisMetAspThrLeuPro     210215220     GlnLysLeuAspLeuLeuLeuSerAspAlaAlaAlaArgPheGlnGly     225230235240     PheLysTyrThrProGluMetLeuArgGluGluValGluAlaTyrLys     245250255     ArgTyrAlaAspArgLeuGluProTyrIleThrAspThrValHisPhe     260265270     IleAsnAspSerIleSerGlnLysLysLysValLeuValGluGlyGly     275280285     GlnAlaThrMetLeuAspIleAspPheGlyThrTyrProPheValThr     290295300     SerSerSerProSerAlaGlyGlyIleCysThrGlyLeuGlyIleAla     305310315320     ProSerValValGlyAspLeuIleGlyValValLysAlaTyrThrThr     325330335     ArgValGlySerGlyProPheProThrGluAsnLeuGlyThrGlyGly     340345350     AspLeuLeuArgLeuAlaGlyGlnGluPheGlyThrThrThrGlyArg     355360365     ProArgArgCysGlyTrpLeuAspIleValAlaLeuLysPheSerCys     370375380     GlnIleAsnGlyPheAlaSerLeuAsnLeuThrLysLeuAspValLeu     385390395400     SerAspLeuAsnGluIleGlnLeuGlyValAlaTyrLysArgSerAsp     405410415     GlyThrProValLysSerPheProGlyAspLeuArgLeuLeuGluGlu     420425430     LeuHisValGluTyrGluValLeuProGlyTrpLysSerAspIleSer     435440445     SerValArgAsnTyrSerAspLeuProLysAlaAlaGlnGlnTyrVal     450455460     GluArgIleGluGluLeuValGlyValProIleHisTyrIleGlyIle     465470475480     GlyProGlyArgAspAlaLeuIleTyrLys     485490     (2) INFORMATION FOR SEQ ID NO:3:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 1835 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (iii) HYPOTHETICAL: NO     (ix) FEATURE:     (A) NAME/KEY: CDS     (B) LOCATION: 18..1469     (D) OTHER INFORMATION: /product= "Maize Adenylosuccinate     Synthetase"     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:     AAAACCCTCCCACCATCATGTCGCTCTCCACACTCAGCCACCCGGCCGCC50     MetSerLeuSerThrLeuSerHisProAlaAla     495500     GCCGCCGCCGGGAGCGGAAAATCCCTTTTCCCGGCTGGCCCGGCGGCG98     AlaAlaAlaGlySerGlyLysSerLeuPheProAlaGlyProAlaAla     505510515     CAGTCCGTACATTTCCCCAAGGCACGGCTCCCTGTCCCCGCCGCCGTC146     GlnSerValHisPheProLysAlaArgLeuProValProAlaAlaVal     520525530     TCCGCCGCTACTGCGGCTGTTCACGCGGAGGATAGGGTTTCGTCGCTG194     SerAlaAlaThrAlaAlaValHisAlaGluAspArgValSerSerLeu     535540545     ACTCAAGTCTCCGGCGTGCTGGGGTCGCAGTGGGGCGACGAGGGAAAG242     ThrGlnValSerGlyValLeuGlySerGlnTrpGlyAspGluGlyLys     550555560565     GGCAAGCTCGTCGACGTGCTCGCCCCCCGCTTCGACATAGTCGCGCGT290     GlyLysLeuValAspValLeuAlaProArgPheAspIleValAlaArg     570575580     TGCCAGGGGGGAGCGAACGCTGGACATACCATCTACAACTCAGAAGGC338     CysGlnGlyGlyAlaAsnAlaGlyHisThrIleTyrAsnSerGluGly     585590595     AAGAAGTTTGCTCTGCATCTTGTTCCATCTGGTATTCTCCATGAAGGG386     LysLysPheAlaLeuHisLeuValProSerGlyIleLeuHisGluGly     600605610     ACACTGTGTGTTGTTGGCAATGGAGCAGTCATCCATGTTCCAGGGTTC434     ThrLeuCysValValGlyAsnGlyAlaValIleHisValProGlyPhe     615620625     TTTGGAGAAATTGATGGTCTTGAGTCCAATGGAGTCCGCTGCGGTGGA482     PheGlyGluIleAspGlyLeuGluSerAsnGlyValArgCysGlyGly     630635640645     AGGATACTGGTATCCGACCGGGCACATCTGCTGTTTGATCTGCACCAG530     ArgIleLeuValSerAspArgAlaHisLeuLeuPheAspLeuHisGln     650655660     GCTGTGGATGGACTTAGGGAAGCAGAGCTTGAAAATTCATTTATAGGG578     AlaValAspGlyLeuArgGluAlaGluLeuGluAsnSerPheIleGly     665670675     ACAACTAAGAGAGGCATTGGTCCTTGTTACTCCAGCAAGGTAACTCGA626     ThrThrLysArgGlyIleGlyProCysTyrSerSerLysValThrArg     680685690     AATGGACTGCGGGTTTGTGATTTACGACACATGGACACTTTTGGGGAT674     AsnGlyLeuArgValCysAspLeuArgHisMetAspThrPheGlyAsp     695700705     AAGCTTGACATCTTATTCAAAGACGCTGCTTCGAGATTTCAAGGCTTT722     LysLeuAspIleLeuPheLysAspAlaAlaSerArgPheGlnGlyPhe     710715720725     CAGTACAGCAAAAGCTTGCTCAAGGAAGAGGTTGAGAGATACAAGAAG770     GlnTyrSerLysSerLeuLeuLysGluGluValGluArgTyrLysLys     730735740     TTTGCTGATCGCTTGGAGCCCTTCATTGCTGATACCGTGCATGTGCTA818     PheAlaAspArgLeuGluProPheIleAlaAspThrValHisValLeu     745750755     AATGAATCTATCAAGCAGAAGAAGAAAATCCTGGTCGAAGGCGGCCAA866     AsnGluSerIleLysGlnLysLysLysIleLeuValGluGlyGlyGln     760765770     GCAACTATGCTGGATATTGATTTTGGCACTTATCCATTTGTGACTTCT914     AlaThrMetLeuAspIleAspPheGlyThrTyrProPheValThrSer     775780785     TCTAGCCCTTCAGCTGGCGGGATATGCACAGGCCTAGGGATTGCTCCA962     SerSerProSerAlaGlyGlyIleCysThrGlyLeuGlyIleAlaPro     790795800805     AGGGCAATTGGCGACCTGATTGGAGTGGTCAAAGCTTACACATCTAGA1010     ArgAlaIleGlyAspLeuIleGlyValValLysAlaTyrThrSerArg     810815820     GTCGGCTCTGGCCCTTTCCCAACTGAACTATTTGGAGAGGAAGGTGAT1058     ValGlySerGlyProPheProThrGluLeuPheGlyGluGluGlyAsp     825830835     CGCCTTAGGAAAGCTGGAATGGAATTTGGCACAACAACAGGTCGCCCA1106     ArgLeuArgLysAlaGlyMetGluPheGlyThrThrThrGlyArgPro     840845850     AGGCGTTGCGGCTGGCTTGACATTGTTGCGCTTAAGCACAGCTGCCAA1154     ArgArgCysGlyTrpLeuAspIleValAlaLeuLysHisSerCysGln     855860865     ATCAATGGGTTCTCATCACTTAATCTGACCAAACTGGATGTTCTGTCC1202     IleAsnGlyPheSerSerLeuAsnLeuThrLysLeuAspValLeuSer     870875880885     GGGTTGTCAGAAATTAAGGTGGGTGTTTCTTATACCCAGACTGATGGA1250     GlyLeuSerGluIleLysValGlyValSerTyrThrGlnThrAspGly     890895900     CAGAAGCTGCAATCCTTCCCTGGGGATCTTGATACCCTTGAGCAAGTA1298     GlnLysLeuGlnSerPheProGlyAspLeuAspThrLeuGluGlnVal     905910915     CAGGTCAACTATGAGGTTCTGCCTGGGTGGCAAAGTGACATTTCTTCT1346     GlnValAsnTyrGluValLeuProGlyTrpGlnSerAspIleSerSer     920925930     GTTCGAAGATACGATGAACTTCCCCAAGCTGCCCGCCTCTATGTGGAG1394     ValArgArgTyrAspGluLeuProGlnAlaAlaArgLeuTyrValGlu     935940945     AGGATAGAAGAACTTGTTGGTGTTCCCGTGCACTACATTGGTGTTGGA1442     ArgIleGluGluLeuValGlyValProValHisTyrIleGlyValGly     950955960965     CCTGGCAGAGATGCTCTCATATACAAGTAAAAGCAACTTTATTTGGT1489     ProGlyArgAspAlaLeuIleTyrLys     970     CCTTGGTTGGGCGGAAACCTGGCCGGGACTCGGGAGCATTTGCATTTTCTTGGCGTGGTA1549     GCTTTTGATACGGTGAAGTCACTGACTCGTGGAGTGATGTTGCTCAATAATCAGAACCTT1609     GTTCTAATACAGCCGCTGAGACATCAGCTAAGGCGAATAAGGGAAGGATGAGTCATTTGC1669     ACCATGTTTGACCACCAATTGTTAGGTGGTCCATATATTTTGTACTAATTGTGAGACTTT1729     GTGCTATGGATCTCAACTGTATACCTTGCTGGTGCATGGCTTTGGGTTTACATGGTTGAA1789     AATGAGATTGGTGTACTAATTGTCTAAAAAAAAAAAAAAAAAAAAA1835     (2) INFORMATION FOR SEQ ID NO:4:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 484 amino acids     (B) TYPE: amino acid     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: protein     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:     MetSerLeuSerThrLeuSerHisProAlaAlaAlaAlaAlaGlySer     151015     GlyLysSerLeuPheProAlaGlyProAlaAlaGlnSerValHisPhe     202530     ProLysAlaArgLeuProValProAlaAlaValSerAlaAlaThrAla     354045     AlaValHisAlaGluAspArgValSerSerLeuThrGlnValSerGly     505560     ValLeuGlySerGlnTrpGlyAspGluGlyLysGlyLysLeuValAsp     65707580     ValLeuAlaProArgPheAspIleValAlaArgCysGlnGlyGlyAla     859095     AsnAlaGlyHisThrIleTyrAsnSerGluGlyLysLysPheAlaLeu     100105110     HisLeuValProSerGlyIleLeuHisGluGlyThrLeuCysValVal     115120125     GlyAsnGlyAlaValIleHisValProGlyPhePheGlyGluIleAsp     130135140     GlyLeuGluSerAsnGlyValArgCysGlyGlyArgIleLeuValSer     145150155160     AspArgAlaHisLeuLeuPheAspLeuHisGlnAlaValAspGlyLeu     165170175     ArgGluAlaGluLeuGluAsnSerPheIleGlyThrThrLysArgGly     180185190     IleGlyProCysTyrSerSerLysValThrArgAsnGlyLeuArgVal     195200205     CysAspLeuArgHisMetAspThrPheGlyAspLysLeuAspIleLeu     210215220     PheLysAspAlaAlaSerArgPheGlnGlyPheGlnTyrSerLysSer     225230235240     LeuLeuLysGluGluValGluArgTyrLysLysPheAlaAspArgLeu     245250255     GluProPheIleAlaAspThrValHisValLeuAsnGluSerIleLys     260265270     GlnLysLysLysIleLeuValGluGlyGlyGlnAlaThrMetLeuAsp     275280285     IleAspPheGlyThrTyrProPheValThrSerSerSerProSerAla     290295300     GlyGlyIleCysThrGlyLeuGlyIleAlaProArgAlaIleGlyAsp     305310315320     LeuIleGlyValValLysAlaTyrThrSerArgValGlySerGlyPro     325330335     PheProThrGluLeuPheGlyGluGluGlyAspArgLeuArgLysAla     340345350     GlyMetGluPheGlyThrThrThrGlyArgProArgArgCysGlyTrp     355360365     LeuAspIleValAlaLeuLysHisSerCysGlnIleAsnGlyPheSer     370375380     SerLeuAsnLeuThrLysLeuAspValLeuSerGlyLeuSerGluIle     385390395400     LysValGlyValSerTyrThrGlnThrAspGlyGlnLysLeuGlnSer     405410415     PheProGlyAspLeuAspThrLeuGluGlnValGlnValAsnTyrGlu     420425430     ValLeuProGlyTrpGlnSerAspIleSerSerValArgArgTyrAsp     435440445     GluLeuProGlnAlaAlaArgLeuTyrValGluArgIleGluGluLeu     450455460     ValGlyValProValHisTyrIleGlyValGlyProGlyArgAspAla     465470475480     LeuIleTyrLys     __________________________________________________________________________ 

We claim:
 1. A nucleotide probe comprising a contiguous portion of at least 10 nucleotides in length of a coding sequence, or a complementary sequence thereto, for adenylosuccinate synthetase enzyme (ADSS) from Arabidopsis or maize, wherein said probe binds specifically to a plant adenylosuccinate synthetase gene or mRNA.
 2. A method for detecting an ADSS gene or mRNA comprising combining the nucleotide probe of claim 1, with an unknown nucleotide sequence under conditions suitable for specific binding of said nucleotide probe to a plant adenylosuccinate synthetase gene or mRNA, and determining whether said nucleotide probe binds specifically to said unknown nucleotide seguence.
 3. The method of claim 2, wherein said probe is derived from a plant ADSS coding sequence selected from the group consisting of Arabidopsis ADSS coding sequence set forth in SEQ ID No. 1, from nucleotide 1 to nucleotide 1471, and maize ADSS coding sequence set forth in SEQ ID No. 3, from nucleotide 18 to nucleotide
 1469. 4. The method of claim 3 wherein the isolated DNA is that set forth in SEQ ID NO:1.
 5. The method of claim 3 wherein the isolated DNA is that set forth in SEQ ID NO:3.
 6. A method for detecting an ADSS gene or mRNA comprising combining a probe of at least 20 nucleotides in length of an isolated DNA molecule selected for the group consisting of Arab idops is ADSS coding sequence set for the in SEQ ID NO:1, from nucleotide 1 to nucleotide 1471, and maize ADSS coding sequence set forth in SEQ ID NO:3, from nucleotide 18 to nucleotide 1469, with an unknown sequence under conditions suitable for specific binding of said probe to a plant adenylosuccinate synthetase gene or mRNA, wherein said probe specifically hybridizes to a plant adenylosuccinate synthetase (ADSS) gene or mRNA after polymerase chain reaction, and determining whether said probe binds specifically to said unknown nucleotide sequence.
 7. The method of claim 6 in which the isolated DNA is that set forth in SEQ ID NO:1.
 8. The method of claim 6 in which the isolated DNA is that set forth in SEQ ID NO:3. 